(i) Field of the Invention
The present invention relates to a motor vehicle seat, and more specially a seat for a commercial vehicle. The seat has an adjustment system for taking into account different weights of persons using the seat, wherein a backrest support plate of the seat is guided for generally capable of upright motion on a backrest support and, between the backrest support plate and the support there is at least one spring for supporting the seat portion, the spring being connected at one end to the backrest support plate or the support by way of an adjustment member capable of compensating for the different drivers' weights.
(ii) The Prior Art
In the case of seat adjustments to a driver's weight, a spring is usually put under a greater or lesser strain by turning a screw-threaded rod and thus adjusting the point at which the spring is joined with the support plate or support. The best adjustment to the weight of the driver or other user is produced when, on driving in the vehicle, the driver's seat is adjusted so that the spring is at its middle position of the overall possible motion of the spring; that is to say, on static adjustment of the spring there will be the same amount of spring motion upwards and downwards. It will readily be seen that such weight adjustment only makes sense when the system will actually be used by the driver and if the seat is so designed that the right adjustment may readily be produced. However, repeated, quick and easy use is not observed with the known weight adjustment systems, because on the one hand the screw-threaded rod has to be turned more than once and this, to the driver, seems to be a waste of time so that no such adjustment is undertaken. Furthermore, it is not readily possible for the driver to see if the spring force adjustment has been adjusted to the right value. For this reason, seats have been designed with a pointer or the like to make it clear when the right adjustment has been produced.
Furthermore, in German Auslegeschrift specification No. 1,245,766 a driver's seat has been proposed, more specifically fo tractors, where adjustment of the spring force is undertaken by a simple lever which is spring-locked into certain given positions. A shortcoming of this known seat design is, however, that it is generally complex in its mechanical design and is likely to malfunction. In fact, the teaching of German Pat. No. 1,245,766 limits its use to seats in which the seat support system, at least in some parts, is turned about a single axis. The teaching of German Pat. No. 1,245,766 may not in fact be used for a seat which is only moved in an upright direction over a support.